Why You Burn Fewer Kilojoules When You’re Tired

Skimp on sleep and your belly may bulge: not getting enough dream time can actually mess with your metabolism, research in the journal Obesity found.

After logging just four hours of sleep a night for five straight nights, people’s resting metabolic rates – the number of kilojoules your body burns while you’re at rest – slowed by nearly three per cent.

The reason why isn’t totally clear, but researchers think it could have to do with homeostasis – basically, your body’s mission to keep everything in balance.

Since you’re awake longer the day of your short sleep, your body compensates by burning fewer kilojoules the following day, says the study's lead study author, Dr Andrea Spaeth.

In fact, one of Spaeth’s earlier studies found that people scarf down as many as 2000kJ following nights when they didn’t get enough sleep, possibly because sleep deprivation revs up hormones that make you feel hungry and dulls hormones that make you feel full.

“Overall, you’re in a positive energy balance, which leads to weight gain over time,” Spaeth says.

The good news, though, is that the effects of your poor sleep habits can be reversed pretty quickly. After just one 12-hour recovery snooze session, the people in Spaeth’s study returned to their normal metabolisms.